Abstract [en]

The purpose of this study is to compare solutions for seam tracking with a welding robot. At the moment the used solution is an external seventh axis made by Permanova which is going to be compared to software made by ABB called EGM. The primary comparisons shall be done regarding the dead time and the time constant of the two processes. A primary problem with this was the uncertainty that comes with ocular inspection of the graphs in order to extract relevant values. Another problem, that also made construing the curves harder, was that there were some disturbances that caused distorted curves. Experiments were done on a model of the actual process, meaning that no welding equipment was connected to the robot in this model process. Instead a laser sensor was mounted onto the robot that measured against a parallel metal block. The seventh axis was connected for all tests to make sure that the results were comparable when it comes to the weight that the robot arm is burdened with. Each experiment had different parameters, such as speed and distance from the robot's base. Several tests were made with the same parameters to make sure that good results were had.

One method used for analysis of gathered data was comparing a similar first order system to the step response of different experiments. The values of this approximate step response were tweaked until both step responses were fairly similar, however, the human factor is very relevant in this analysis.

The results showed a clear advantage towards Permanova's seventh axis in both decreased dead time and time constant. For example, the filtered mean value for the dead time with EGM was 266 ms and a standard deviation of 20,8 ms, while Permanova clocked in at 11,5 ms with a standard deviation of 2,0 ms. The filtered time constants followed the same trend and were at 68 ms, standard deviation of 13,5 ms, for EGM and 33 ms, standard deviation of 4,8 ms, for Permanova. It was quite surprising how big the difference was between EGM and Permanova's seventh axis, but the seventh axis was without a doubt the solution best suited to this kind of process. Due to the lacking performance from EGM it is determined to be unfit for laser welding applications at PTW.